It has long been desired to provide a high-definition television picture that approaches the quality of a projected 35 millimeter photographic film image. See, for example, Image Quality, "A Comparison of Photographic and Television Systems," Otto H. Schade, Jr., RCA Corporation, 1975.
An approach to providing high-definition television that could be received as a conventional television picture by conventional television receivers operating according to the Natioal Television Standards Committee (NTSC) requirements or could be received as a high-definition television picture by newly designed receivers without requiring prohibitively large bandwidth is disclosed in an article entitled, "A Compatible High-Definition Television System", by T. S. Rzeszewski, The Bell System Technical Journal, Vol. 62, No. 7, September 1983, pp. 2091-2111. In that system, the high-frequency luminance and chrominance information and the conventional luminance and chrominance information are combined into a baseband signal before being modulated by a carrier for the transmission of the baseband signal on two television channels. This system is particularly applicable to high-power transmitters such as used by commercial television stations since the signal to be transmitted is first formed at the baseband level and then modulated and amplified for transmission. Whereas the system proposed by Rzeszewski appears to be applicable for broadcast television, it does have the disadvantage of requiring expensive encoders at the transmitter and expensive decoders in each individual TV receiver.
The article by E. W. Herold, entitled, "A Compatible High-Resolution TV System for Cablecasting", Proceedings of the IEEE, Vol. 58, No. 7, July, 1970, pp. 1013-1015, suggests that the luminance portion of the TV display can be improved for low-power applications by using an adjacent channel to communicate additional luminance information. However, the latter article does not disclose a method for including the additional luminance information; nor does it indicate a method for improving the chrominance information, for reducing cross-effects between the chrominance and luminance information, or for separating the chrominance and luminance information when modulated and amplified to transmission and power levels.
Therefore, there exists a need for an economical high-definition television system that provides both improved luminance and chrominance information, that reduces cross-effects, and is compatible with NTSC type TV receivers. Such a system would find wide-spread use in low-power applications such as home cable delivery systems or intercampus video networks such as those proposed for large university campuses or corporation headquarters.